scholarly journals Water masses as a unifying framework for understanding the Southern Ocean Carbon Cycle

2011 ◽  
Vol 8 (5) ◽  
pp. 1031-1052 ◽  
Author(s):  
D. Iudicone ◽  
K. B. Rodgers ◽  
I. Stendardo ◽  
O. Aumont ◽  
G. Madec ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
Water Mass ◽  
Water Masses ◽  
Global Ocean ◽  
Intermediate Water ◽  
Formation Processes ◽  
Carbon Cycle Model ◽  
Carbon Transfer

Abstract. The scientific motivation for this study is to understand the processes in the ocean interior controlling carbon transfer across 30° S. To address this, we have developed a unified framework for understanding the interplay between physical drivers such as buoyancy fluxes and ocean mixing, and carbon-specific processes such as biology, gas exchange and carbon mixing. Given the importance of density in determining the ocean interior structure and circulation, the framework is one that is organized by density and water masses, and it makes combined use of Eulerian and Lagrangian diagnostics. This is achieved through application to a global ice-ocean circulation model and an ocean biogeochemistry model, with both components being part of the widely-used IPSL coupled ocean/atmosphere/carbon cycle model. Our main new result is the dominance of the overturning circulation (identified by water masses) in setting the vertical distribution of carbon transport from the Southern Ocean towards the global ocean. A net contrast emerges between the role of Subantarctic Mode Water (SAMW), associated with large northward transport and ingassing, and Antarctic Intermediate Water (AAIW), associated with a much smaller export and outgassing. The differences in their export rate reflects differences in their water mass formation processes. For SAMW, two-thirds of the surface waters are provided as a result of the densification of thermocline water (TW), and upon densification this water carries with it a substantial diapycnal flux of dissolved inorganic carbon (DIC). For AAIW, principal formatin processes include buoyancy forcing and mixing, with these serving to lighten CDW. An additional important formation pathway of AAIW is through the effect of interior processing (mixing, including cabelling) that serve to densify SAMW. A quantitative evaluation of the contribution of mixing, biology and gas exchange to the DIC evolution per water mass reveals that mixing and, secondarily, gas exchange, effectively nearly balance biology on annual scales (while the latter process can be dominant at seasonal scale). The distribution of DIC in the northward flowing water at 30° S is thus primarily set by the DIC values of the water masses that are involved in the formation processes.

scholarly journals Water Mass Analysis of Effect of Climate Change on Air–Sea CO2 Fluxes: The Southern Ocean

2012 ◽  
Vol 25 (11) ◽  
pp. 3894-3908 ◽  
Author(s):  
Roland Séférian ◽  
Daniele Iudicone ◽  
Laurent Bopp ◽  
Tilla Roy ◽  
Gurvan Madec
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
Large Scale ◽  
Climate Model ◽  
Water Mass ◽  
Water Masses ◽  
Biogeochemical Model ◽  
Carbon Uptake ◽  
Intermediate Water

Impacts of climate change on air–sea CO2 exchange are strongly region dependent, particularly in the Southern Ocean. Yet, in the Southern Ocean the role of water masses in the uptake of anthropogenic carbon is still debated. Here, a methodology is applied that tracks the carbon flux of each Southern Ocean water mass in response to climate change. A global marine biogeochemical model was coupled to a climate model, making 140-yr Coupled Model Intercomparison Project phase 5 (CMIP5)-type simulations, where atmospheric CO2 increased by 1% yr−1 to 4 times the preindustrial concentration (4 × CO2). Impacts of atmospheric CO2 (carbon-induced sensitivity) and climate change (climate-induced sensitivity) on the water mass carbon fluxes have been isolated performing two sensitivity simulations. In the first simulation, the atmospheric CO2 influences solely the marine carbon cycle, while in the second simulation, it influences both the marine carbon cycle and earth’s climate. At 4 × CO2, the cumulative carbon uptake by the Southern Ocean reaches 278 PgC, 53% of which is taken up by modal and intermediate water masses. The carbon-induced and climate-induced sensitivities vary significantly between the water masses. The carbon-induced sensitivities enhance the carbon uptake of the water masses, particularly for the denser classes. But, enhancement strongly depends on the water mass structure. The climate-induced sensitivities either strengthen or weaken the carbon uptake and are influenced by local processes through changes in CO2 solubility and stratification, and by large-scale changes in outcrop surface (OS) areas. Changes in OS areas account for 45% of the climate-induced reduction in the Southern Ocean carbon uptake and are a key factor in understanding the future carbon uptake of the Southern Ocean.

scholarly journals Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania

2017 ◽  
Author(s):  
Paula C. Pardo ◽  
Bronte Tilbrook ◽  
Clothilde Langlais ◽  
Tom W. Trull ◽  
Steve R. Rintoul
Keyword(s):  
Southern Ocean ◽  
Water Mass ◽  
Dissolved Inorganic Carbon ◽  
Water Masses ◽  
Atmospheric Co2 ◽  
Positive Trend ◽  
Intermediate Water ◽  
Mode Water ◽  
Aragonite Saturation ◽  
Deep Waters

Abstract. Biogeochemical change in the water masses of the Southern Ocean, south of Tasmania, was assessed for the 16-year period between 1995 and 2011 using data from 4 summer repeats of the WOCE/JGOFS/CLIVAR/GO-SHIP SR03 hydrographic section (at ~ 140° E). Changes in temperature, salinity, oxygen, and nutrients were used to disentangle the effect of solubility, biology, circulation and anthropogenic carbon (CANT) uptake on the variability of dissolved inorganic carbon (DIC) for 8 water mass layers defined by neutral surfaces (ϒn). CANT was estimated using an improved back-calculation method. Warming (~ 0.0352 ± 0.0170 °C yr−1) of Subtropical Central Water (STCW) and Antarctic Surface Water (AASW) layers decreased their gas solubility, and accordingly DIC concentrations increased less rapidly than expected from equilibration with rising atmospheric CO2 (~ 0.86 ± 0.16 μmol kg−1 yr−1 versus ~ 1 ± 0.12 μmol kg−1 yr−1). An increase in apparent oxygen utilisation (AOU) occurred in these layers due to either remineralization of organic matter or intensification of upwelling. The range of estimates for the increases of CANT were 0.71 ± 0.08 to 0.93 ± 0.08 μmol kg−1 yr−1 for STCW and 0.35 ± 0.14 to 0.65 ± 0.21 μmol kg−1 yr−1 for AASW, with the lower values in each water mass obtained by assigning all the AOU change to remineralization. DIC increases in the Sub-Antarctic Mode Water (SAMW, 1.10 ± 0.14 μmol kg−1 yr−1) and Antarctic Intermediate Water (AAIW, 0.40 ± 0.15 μmol kg−1 yr−1) layers were similar to the calculated CANT trends. For SAMW, the CANT increase tracked rising atmospheric CO2. As a consequence of the general DIC increase, decreases in total pH (pHT) and aragonite saturation (ΩAr) were found in most water masses, with the upper ocean and the SAMW layer presenting the largest trends for pHT decrease (~ −0.0031 ± 0.0004 yr−1). DIC increases in deep and bottom layers (~ 0.24 ± 0.04 μmol kg−1 yr−1) resulted from the advection of old deep waters to resupply increased upwelling, as corroborated by increasing silicate (~ 0.21 ± 0.07 μmol kg−1 yr−1), which also reached the upper layers near the Antarctic Divergence (~ 0.36 ± 0.06 μmol kg−1 yr−1) and was accompanied by an increase in salinity. The observed changes in DIC over the 16-year span caused a shoaling (~ 340 m) of the aragonite saturation depth (ASD, ΩAr = 1) within Upper Circumpolar Deep Water that followed the upwelling path of this layer. From all our results, we conclude a scenario of increased transport of deep waters into the section and enhanced upwelling at high latitudes for the period between 1995 and 2011, probably linked to a positive trend in the Southern Annular Mode. Although enhanced upwelling lowered the capacity of the AASW layer to uptake atmospheric CO2, it did not limit that of the newly forming SAMW and AAIW, which exhibited CANT storage rates (~ 0.41 ± 0.20 mol m−2 yr−1) twice that of the upper layers.

scholarly journals Water masses in the Atlantic Ocean: characteristics and distributions

Ocean Science ◽  
2021 ◽  
Vol 17 (2) ◽  
pp. 463-486
Author(s):  
Mian Liu ◽  
Toste Tanhua
Keyword(s):  
Atlantic Ocean ◽  
Deep Water ◽  
Bottom Water ◽  
Water Mass ◽  
Sea Water ◽  
Weddell Sea ◽  
Water Masses ◽  
Global Ocean ◽  
Intermediate Water ◽  
The North

Abstract. A large number of water masses are presented in the Atlantic Ocean, and knowledge of their distributions and properties is important for understanding and monitoring of a range of oceanographic phenomena. The characteristics and distributions of water masses in biogeochemical space are useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples. Here, we define the characteristics of the major water masses in the Atlantic Ocean as source water types (SWTs) from their formation areas, and map out their distributions. The SWTs are described by six properties taken from the biased-adjusted Global Ocean Data Analysis Project version 2 (GLODAPv2) data product, including both conservative (conservative temperature and absolute salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) properties. The distributions of these water masses are investigated with the use of the optimum multi-parameter (OMP) method and mapped out. The Atlantic Ocean is divided into four vertical layers by distinct neutral densities and four zonal layers to guide the identification and characterization. The water masses in the upper layer originate from wintertime subduction and are defined as central waters. Below the upper layer, the intermediate layer consists of three main water masses: Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Water (MW). The North Atlantic Deep Water (NADW, divided into its upper and lower components) is the dominating water mass in the deep and overflow layer. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW). The Antarctic Bottom Water (AABW) is the only natural water mass in the bottom layer, and this water mass is redefined as Northeast Atlantic Bottom Water (NEABW) in the north of the Equator due to the change of key properties, especially silicate. Similar with NADW, two additional water masses, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea region in order to understand the origin of AABW.

scholarly journals Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring

2013 ◽  
Vol 10 (9) ◽  
pp. 15033-15076 ◽  
Author(s):  
K. B. Rodgers ◽  
O. Aumont ◽  
S. E. Mikaloff Fletcher ◽  
Y. Plancherel ◽  
L. Bopp ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Ad Hoc ◽  
Global Ocean ◽  
Nutrient Concentrations ◽  
Carbon Uptake ◽  
Carbon Cycle Model ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon ◽  
The Impact

Abstract. Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model. The objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000–2006, with differences of order 0.9 Pg C yr−1 over the region south of 45° S. Wind stirring impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other species associated with ocean biogeochemistry. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong sensitivity of nutrient concentrations exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry, through its impact over the Southern Ocean.

Reshuffling of Nutrients in the Southern Ocean

2020 ◽  
Author(s):  
Ivy Frenger ◽  
Ivana Cerovecki ◽  
Matthew Mazloff
Keyword(s):  
Southern Ocean ◽  
Water Mass ◽  
Driving Forces ◽  
Water Masses ◽  
Global Ocean ◽  
Upper Ocean ◽  
Physical Processes ◽  
Near Surface ◽  
Deep Waters ◽  
Ocean Productivity

<p>Deep waters upwell in the Southern Ocean, replete with nutrients. Some of these nutrients enter lighter mode and intermediate waters (MIW), fueling upper ocean productivity in the otherwise nutrient depleted (sub)tropical waters. However some of the upwelled nutrients are retained in the Southern Ocean or leak into denser bottom waters (AABW), making them unavailable for upper ocean productivity. Despite its fundamental importance for the global ocean productivity, this “reshuffling” of nutrients between Southern Ocean water masses, and its driving forces and temporal variability, have not been quantified to date.</p><p>We analyze the globally major limiting macronutrient, nitrate (NO<sub>3</sub>), using the results of a data-assimilating coupled ocean-sea-ice and biogeochemistry model, the Biogeochemical Southern Ocean State Estimate (B-SOSE), for the years 2008 – 2017. Using a water mass framework, applied to five day averaged SOSE output south of 30<sup>o</sup>S, we quantify the processes controlling NO<sub>3</sub> inventories and fluxes. The water mass framework enables us to assess the relative importance of physical processes (such as surface buoyancy fluxes and diapycnal mixing) and biogeochemical processes (such as productivity and remineralization) in driving the transfer of NO<sub>3</sub> from upwelling deep waters (CDW) to MIW and AABW, and its interannual variability.</p><p>Our results show that two thirds of the NO<sub>3</sub> supplied to MIW occurs through lightening, or transforming, of CDW waters during the course of the overturning circulation. The other third of the NO<sub>3</sub> supplied to MIW occurs through upward mixing of NO<sub>3</sub> from NO<sub>3</sub>-enriched CDW. This means that physical processes determine the mean MIW NO<sub>3</sub> content. Biology does not have a net effect on MIW NO<sub>3</sub>: while biological uptake draws down the MIW concentration of  NO<sub>3</sub> near the surface, remineralization of organic matter compensates for this MIW loss below the surface. Also, we find that the productivity in the subtropical waters south of 30<sup>o</sup>S is fed through both, the canonical upward mixing of NO<sub>3</sub> through the thermocline, and through the near surface supply from MIW. Thus, again, water mass transformation is playing a large role in nutrient distributions. </p><p>In ongoing work, we assess the drivers of variability of the reshuffling of NO<sub>3</sub> between water masses and their potential sensitivity to climate change.</p>

Southern Ocean water mass properties and circulation under CMIP6 climate forcing

2021 ◽  
Author(s):  
Andrew Meijers ◽  
David Munday ◽  
Tilla Roy ◽  
Jean-Baptiste Sallée
Keyword(s):  
Southern Ocean ◽  
Water Mass ◽  
Dissolved Inorganic Carbon ◽  
Heat Content ◽  
Water Masses ◽  
Climate Forcing ◽  
Intermediate Water ◽  
Ocean Water ◽  
Mode Water ◽  
Mass Properties

<p>We examine the representation of Southern Ocean water mass properties, circulation and transformation in an ensemble of CMIP6 models, under historical climate forcing conditions and under a range of future climate scenarios. By using a dynamically defined water mass classification scheme based on physical characteristics (salinity minimum, potential vorticity minimum etc) rather than fixed water mass properties, we are able to compare water masses across a range of models, often with significant water mass property differences, as well as within single models where water mass properties change under climate forcing. We find that under strong climate forcing scenarios (ssp585) the heat content of SubAntarctic Mode Water (SAMW), Antarctic Intermediate Water (AAIW) and Circumpolar Deep Water (CDW) all increase consistently across models, while Antarctic Bottom Water (AABW) does not change significantly. Importantly this change is strongly modulated by using dynamic definitions. Both SAMW and AAIW lighten significantly in density, and using time varying definitions their volumes remain relatively constant, whereas using a time invariant definition both experience extremely significant increases in volume and heat content. We show that dynamically it is the ocean interior, CDW and AAIW, that dominate heat uptake under strong forcing. Similarly, dissolved inorganic carbon uptake occurs predominantly in the CDW. In contrast AABW volumes decrease significantly.</p><p>There is a consistent ‘fingerprint’ of temperature change in density space across all models under strong forcing scenarios, with CDW experiencing surface intensified warming as it shoals to the south, and SAMW/AAIW demonstrating cooling and freshening in their subducted layers and a uniform warming in the surface layers. We show that the upper cell of the residual overturning circulation (calculated with the new availability of eddy parametrisation terms in CMIP6) consistently increases across all models evaluated, by 10-50% (up to 10 Sv in some models), while the lower cell is dramatically decreased in strength, declining by up to 70% in some models. We provide evidence that surface warming may be modulated by increased eddy driven upwelling, as well as surface freshening driving the shutdown of AABW formation. Finally we compute a Walin water mass budget, balancing surface forcing, interior storage and meridional export and inferring interior mixing between water masses, and contrast all findings with similar analyses in CMIP5.</p><p> </p>

scholarly journals Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring

2014 ◽  
Vol 11 (15) ◽  
pp. 4077-4098 ◽  
Author(s):  
K. B. Rodgers ◽  
O. Aumont ◽  
S. E. Mikaloff Fletcher ◽  
Y. Plancherel ◽  
L. Bopp ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Ad Hoc ◽  
Global Ocean ◽  
Relative Reduction ◽  
Carbon Uptake ◽  
Carbon Cycle Model ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon ◽  
The Impact

Abstract. Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model, where the objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000–2006, with a relative reduction with wind stirring on the order of 0.9 Pg C yr−1 over the region south of 45° S. This impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other ocean biogeochemical tracers. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong reduction on the order of 25–30% in the concentrations of NO3 exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry through its impact over the Southern Ocean.

scholarly journals Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania

2017 ◽  
Vol 14 (22) ◽  
pp. 5217-5237 ◽  
Author(s):  
Paula Conde Pardo ◽  
Bronte Tilbrook ◽  
Clothilde Langlais ◽  
Thomas William Trull ◽  
Stephen Rich Rintoul
Keyword(s):  
Southern Ocean ◽  
Water Mass ◽  
Dissolved Inorganic Carbon ◽  
Water Masses ◽  
Atmospheric Co2 ◽  
Intermediate Water ◽  
Mode Water ◽  
Aragonite Saturation ◽  
Deep Waters ◽  
Using Data

Abstract. Biogeochemical change in the water masses of the Southern Ocean, south of Tasmania, was assessed for the 16-year period between 1995 and 2011 using data from four summer repeats of the WOCE–JGOFS–CLIVAR–GO-SHIP (Key et al., 2015; Olsen et al., 2016) SR03 hydrographic section (at ∼ 140° E). Changes in temperature, salinity, oxygen, and nutrients were used to disentangle the effect of solubility, biology, circulation and anthropogenic carbon (CANT) uptake on the variability of dissolved inorganic carbon (DIC) for eight water mass layers defined by neutral surfaces (γn). CANT was estimated using an improved back-calculation method. Warming (∼ 0.0352 ± 0.0170 °C yr−1) of Subtropical Central Water (STCW) and Antarctic Surface Water (AASW) layers decreased their gas solubility, and accordingly DIC concentrations increased less rapidly than expected from equilibration with rising atmospheric CO2 (∼ 0.86 ± 0.16 µmol kg−1 yr−1 versus ∼ 1 ± 0.12 µmol kg−1 yr−1). An increase in apparent oxygen utilisation (AOU) occurred in these layers due to either remineralisation of organic matter or intensification of upwelling. The range of estimates for the increases in CANT were 0.71 ± 0.08 to 0.93 ± 0.08 µmol kg−1 yr−1 for STCW and 0.35 ± 0.14 to 0.65 ±  0.21 µmol kg−1 yr−1 for AASW, with the lower values in each water mass obtained by assigning all the AOU change to remineralisation. DIC increases in the Sub-Antarctic Mode Water (SAMW, 1.10 ± 0.14 µmol kg−1 yr−1) and Antarctic Intermediate Water (AAIW, 0.40 ± 0.15 µmol kg−1 yr−1) layers were similar to the calculated CANT trends. For SAMW, the CANT increase tracked rising atmospheric CO2. As a consequence of the general DIC increase, decreases in total pH (pHT) and aragonite saturation (ΩAr) were found in most water masses, with the upper ocean and the SAMW layer presenting the largest trends for pHT decrease (∼ −0.0031 ± 0.0004 yr−1). DIC increases in deep and bottom layers (∼ 0.24 ± 0.04 µmol kg−1 yr−1) resulted from the advection of old deep waters to resupply increased upwelling, as corroborated by increasing silicate (∼ 0.21 ± 0.07 µmol kg−1 yr−1), which also reached the upper layers near the Antarctic Divergence (∼ 0.36 ± 0.06 µmol kg−1 yr−1) and was accompanied by an increase in salinity. The observed changes in DIC over the 16-year span caused a shoaling (∼ 340 m) of the aragonite saturation depth (ASD, ΩAr =  1) within Upper Circumpolar Deep Water that followed the upwelling path of this layer. From all our results, we conclude a scenario of increased transport of deep waters into the section and enhanced upwelling at high latitudes for the period between 1995 and 2011 linked to strong westerly winds. Although enhanced upwelling lowered the capacity of the AASW layer to uptake atmospheric CO2, it did not limit that of the newly forming SAMW and AAIW, which exhibited CANT storage rates (∼ 0.41 ± 0.20 mol m−2 yr−1) twice that of the upper layers.

scholarly journals Water mass distributions and transports for the 2014 GEOVIDE cruise in the North Atlantic

2018 ◽  
Vol 15 (7) ◽  
pp. 2075-2090 ◽  
Author(s):  
Maribel I. García-Ibáñez ◽  
Fiz F. Pérez ◽  
Pascale Lherminier ◽  
Patricia Zunino ◽  
Herlé Mercier ◽  
...  
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Water Levels ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Intermediate Water ◽  
North East ◽  
The North ◽  
The North Atlantic

Abstract. We present the distribution of water masses along the GEOTRACES-GA01 section during the GEOVIDE cruise, which crossed the subpolar North Atlantic Ocean and the Labrador Sea in the summer of 2014. The water mass structure resulting from an extended optimum multiparameter (eOMP) analysis provides the framework for interpreting the observed distributions of trace elements and their isotopes. Central Waters and Subpolar Mode Waters (SPMW) dominated the upper part of the GEOTRACES-GA01 section. At intermediate depths, the dominant water mass was Labrador Sea Water, while the deep parts of the section were filled by Iceland–Scotland Overflow Water (ISOW) and North-East Atlantic Deep Water. We also evaluate the water mass volume transports across the 2014 OVIDE line (Portugal to Greenland section) by combining the water mass fractions resulting from the eOMP analysis with the absolute geostrophic velocity field estimated through a box inverse model. This allowed us to assess the relative contribution of each water mass to the transport across the section. Finally, we discuss the changes in the distribution and transport of water masses between the 2014 OVIDE line and the 2002–2010 mean state. At the upper and intermediate water levels, colder end-members of the water masses replaced the warmer ones in 2014 with respect to 2002–2010, in agreement with the long-term cooling of the North Atlantic Subpolar Gyre that started in the mid-2000s. Below 2000 dbar, ISOW increased its contribution in 2014 with respect to 2002–2010, with the increase being consistent with other estimates of ISOW transports along 58–59° N. We also observed an increase in SPMW in the East Greenland Irminger Current in 2014 with respect to 2002–2010, which supports the recent deep convection events in the Irminger Sea. From the assessment of the relative water mass contribution to the Atlantic Meridional Overturning Circulation (AMOC) across the OVIDE line, we conclude that the larger AMOC intensity in 2014 compared to the 2002–2010 mean was related to both the increase in the northward transport of Central Waters in the AMOC upper limb and to the increase in the southward flow of Irminger Basin SPMW and ISOW in the AMOC lower limb.

Sign in / Sign up

Export Citation Format

Share Document